Vacuum tube oscillator



Jan. 7, 1936. R. E. FURAY 2,027,160

' VACUUM TUBE OSCILLATOR Original Filed Jan. 18, 1932 PW? .URRENT.-' J;

CONTROL VOLTAGE.

IN VEN TOR RICHARD FURAK" ATTORNEY Patented Jan. 7, 1936 VACUUM TUBEOSCILLATOR Richard E. Furay, San Francisco, Calif.

Application January 18, 1932, Serial No. 587,230 Renewed September 26,1933 17 Claims.

an oscillator wherein the frequency-determining 1o circuit is not calledupon to supply current to the load circuit; to provide an oscillatorwherein the frequency-determining circuit is substantially symmetrical;to provide a vacuum tube oscillator wherein the load imposed on the tubeby the os- 15 cillating circuit is substantially constant through outthe cycle of-oscillation; to provide a vacuum tube oscillator whereinthe potential of the control elements is automatically varied tocompensate for changes of anode potential; and, con- 20 sequently, toprovide an oscillator which is substantially unaffected in frequency byrelatively large changes of supply current and potential.

Other objects of this invention will be apparent or will be specificallypointed out in.the descrip- 25 tion forming a part of thisspecification, but I do not limit myself to the embodiment of theinvention herein described, as various forms may be adopted within thescope of the claims.

Referring to the drawing:

30 Figure 1 is a vertical sectional view of the vacuum tube of myinvention.

Figure 2 is a plan view of the tube elements, the plane of projectionbeing indicated by the line 2--2 of Figure 1. e

Figure 3 is a schematic circuit diagram of the oscillating circuit of myinvention, embodying the tube shown in the first two figures.

Figure 4 shows the characteristic curves of the tube, indicating theoperating range thereof when 40 used in the circuit of Figure 3.

My invention comprises an oscillator embody- V in a vacuum tube having aplurality of control elements which may be operated so that changes inthe potential thereof have opposite effects upon 45 the plate current,i. e., wherein the negative swing of potential of one of the controlelements increases the output current, while a similar swing of theother element decreases the output current. The two control elements areconnected by a par- 50 allel-tuned circuit, which is coupled to theplate of the oscillator tube. The frequency of oscillation is determinedalmost wholly by the tuning of the parallel circuit connecting the twocontrol elements. The tube preferably used comprises 55 the usualfilament, plate, and grid-control e1ement mounted between filament andplate, and an additional control element, which I have termed areflector, positioned on the opposite side of the filament from theplate. When operated at a proper positive potential the two 5 controlelements have opposite effects on the plate current, as above stated.This positive potential is preferably derived from the plate circuitthrough a resistor. With this arrangement the control-element potentialis a function of the plate potential, varying with it in such a mannerthat variations in plate current or voltage are almost completelycompensated and a high degree of frequency stability is secured eventhough the supply sources feedingthe tube may vary. '15

A preferred form of my device utilizes a tube havingthe usual envelope Ihaving a stem 2 upon which the elements of the tube are mounted. Sealedthrough the stem are a pair of filament leads 3, 4, a plate support andlead 5, and a grid support andlead 6. The stem also carries a' pluralityof supports or dummies I, 9, I0 and H, to which are attached the variouselements of the tube as will be described.

The supports 6, 1,9 and II extend toward the top of the tube to abovethe elements, and secured to their upper ends are a pair of insulatingbars I2, preferably of glass, which tie the supports together to form arigid structure, and to each of these bars is secured a spring hook I 4.

The filamentary cathode I5 of the tube is mounted substantially in aplane, and extends from the lead 3 up over one of the hooks l4, thencetoward the stem 2 where it is hooked over a dummy l6 mounted in thestem, thence up and over the second hook I4 and back to the lead 4.

The plate I1 is positioned substantially parallel to the filament and ismounted on the lead 5 and dummy or support II), the top of the platebeing steadied. by the short wires l9 which are 40 sealed into theinsulating bars I2. I

A planar grid 20 is positioned between the cathode and the plate, andcomprises parallel wires extending between supports 6 and 9. This gridacts in the manner familiar in the ordinary triode construction, and cantake almost any of the many forms which have been developed for thispurpose.

Positioned on the opposite side of the filament from the grid is thecontrol plate or reflector 2 I, which is secured to the wires I and I I.The lead to this element, in the form of the device here shown, is awire 22 which is sealed through the tip 24 of the tube.

The two control elements 20 and 2| are symmetrically placed with respectto the plate, and hence have different effects upon the plate current asis shown by the curves of Figure 4. The curve 25 illustrates the effectof varying the potential of the grid 20 with the reflector main tainedat zero potential. Curve 26 shows the effect on the plate current ofvarying reflector potentials with the grid maintained at zero. Withdifferent potentials on either control a family of curves may be drawnfor the other control element, each curve of the family beingsubstantially parallel to the others and having maxima and minima atsubstantially the same control voltages, although these maxima andminima are of different values for the different curves.

It will be seen that for relatively lowcontrol voltages the effect ofthe two control elements is in the same direction, i. e., for voltagesless than those indicated by the dotted line a the plate currentincreases with increasing potential. At the control voltage a and above,increasing the potential of the reflector decreases the plate current,Whereas increasing the grid potential increases the plate current. At amuch higher positive potential the effect of increasing the gridpotential also reverses, in the range higher than that indicated by thedotted line b of the graph. The operating range of this device isbetween the control voltages indicated by the lines a and b.

The tube is preferably operated in a circuit whose preferred form isshown in Figure 3. The filament I5 is heated by a suitable source 33.The grid 2!] and reflector 2! are connected at opposite ends of aparallel-tuned circuit comprising an inductance coil 3! and variablecondenser 32. The plate I! is connected through a second parallel-tunedcircuit, comprising an inductance 34 and variable condenser 35, to asuitable plate supply 36 and thence back to the filament. The twoparallel-tuned circuits are coupled, preferably by means of a highresistance 3! shunted by a by-pass condenser 39, this coupling circuitbeing preferably connected to the two inductances by variable taps 40and 4! respectively.

Since both of the control elements are operated at positive potential,each of these elements will draw current. This current, flowing throughthe resistor 31, causes a potential drop, so that the control elementsoperate at a potential lower than the plate but which is a definitefunction of the plate potential. The magnitude of this resistor and thepotential drop will, of course, vary with the size of the tube and withthe plate potential, but the correct size for this resistor may readilybe deduced from the operating characteristics of the particular tube,the resistor being so chosen as to bring the mean operating potential ofthe two control elements midway between the control potentials a and bof Figure 4.

The positive control element potential also has the effect of reducingthe output impedance of the tube to a much lower value than would obtainwith a tube of comparable dimensions operated at a negative bias. Thisleads to high plate circuit efiiciency, and, since the mean controlpotential is substantially constant, does not introduce wave formdistortions which are objectionable.

Since the filament, which may be considered as ground potential,operates midway between the grid and the reflector, there will be a nodeof potential approximately midway between the ends of the coil 3|. Theadjustable tap M is displacedslightly from this potential node. Thecoupling of the two oscillating circuits is determined by the positionof both of the taps M3 and ll, these taps being preferably positioned togive the minimum coupling at which stable operation occurs.

In the operation of the device the frequency is determined almostentirely by the tuning of the parallel tank circuit comprising theinductor 3i and condenser 32, it being possible to vary the tuning ofthe plate circuit through wide limits without material frequencyvariations. The effect of the plate circuit tuning does, of course, varythe intensity of the oscillation and the energy output, but until thiscircuit is thrown so far out of tune that the coupling back to thecontrol tank circuit is almost entirely out of phase, oscillation willstill take place with a frequency variation of substantially nil.

The control element circuit is, in fact, almost self-oscillatory. Thecurrent drawn from this circuit is only that to the control elementsofthe tube, however, and since these elements are varying in oppositedirections at the same time this load is substantially a constantregardless of the oscillating power withdrawn from the plate circuit ofthe device. cient to account for the remarkable frequency stability ofthe circuit, and the supply of the positive grid potential as a functionof the plate voltage is a factor which increases this stability.

In practice the device has been found to work :1

pacity of the two control electrodes in opposite 5 directions, so thatthe net input capacity of the tube varies little with changing load.

Those familiar with modern vacuum tube practice will at once recognizethat various modifications in the method of coupling the tuned circuitsand in applying the positive of bias to the control element are possiblewithout affecting the operation of this device. I therefore do notdesire to be limited by the exact form shown, but wish to protect theinvention as defined in the following claims.

I claim:

1. A vacuum tube oscillator comprising the combination with a vacuumtube having an output electrode and a pair of control electrodes, of 1means for biasing said control electrodes to produce opposite effects onthe magnitude of current flow through the tube tosaid output electrodewith similar variations of control potential, 2.

parallel resonant circuit connecting said control electrodes, and aresonant circuit in series with said output electrode and coupled'tosaid first mentioned circuit.

2. A vacuum tube oscillator comprising the combination with a vacuumtube having an output electrode and a pair of control electrodes, ofmeans for biasing said control electrodes to produce opposite effects oncurrent flow through the tube to said output electrode, a parallelresonant circuit connecting said control electrodes, a resonant circuitin series with said output electrode, and a connection joining non-nodalpoints of said circuits.

3. A vacuum tube oscillator comprisingthe combination with a vacuum tubehaving an outi This fact is, of itself, sufiia parallel resonant circuitconnecting'said control electrodes, a resonant circuit in serieswithsaid output electrode, means for maintaining said output electrodeat a positive potential, and a resistive connection between saidresonant circuits for coupling said circuits and maintaining saidcontrol electrodes at a lower mean positive potential to produceopposite effects on current flow through the tube to said outputelectrode.

4. An oscillator comprising the combination with a vacuum tube having acathode, an anode,

a grid control electrode, and an additional control electrode, of aparallel resonant circuit connecting said control electrodes, a secondparallel resonant circuit in series with said anode, a resistorconnecting said circuits intermediate their ends for supplying apositive potential lower than the anode potential to said controlelectrodes to produce opposite effects on current flow through said tubeto said anode, and a condenser bridging said resistor for coupling saidcircuits.

5. The combination with a vacuum tube having a cathode, a platepositioned on one side of said cathode, a control grid between saidcathode and plate, and a second control element in the form of areflector on the opposite side of said cathode, of an oscillatingcircuit comprising. a parallel resonant circuit connecting said grid andreflector, a second parallel resonant circuit in series with said plateand said cathode, means for maintaining said plate at a positivepotential, means for maintaining said reflector at a lower positivepotential to produce a current between said cathode and anode inopposite sense to said grid, andmeans for coupling said parallelresonant circuits.

6. The method of producing electrical oscillations having a high degreeof frequency stability which includes the steps of generating anelectron fiow, causing said fiow'to produce two oppositely varyingcontrol potentials, governing said flow with said potentials, andmaintaining said potentials within a range wherein opposite variationsof said potentials produce like effects on the magnitude of said flow.

7. The method of utilizing a vacuum tube having two control electrodesto produce electrical oscillations having a high degree of frequencystability which includes the steps of causing an electron flow withinsaid tube, maintaining bias potentials 'on said control electrodes suchthat opposite changes in said potentials will produce like effects onthe magnitude of said flow, and

- causing variations in said flow to vary oppositely the potentials ofsaid control electrodes.

8. The method of producing electrical oscilla- 4 tions having a highdegree of frequency stability which comprises the steps of establishingan electron flow, causing variations in magnitude of said'fiow toproduce two oppositely varying potentials and causing said potentialscumulatively to effect said changes in magnitude of flow.

9. The method of producing electrical oscilla- L tions having a highdegree of frequency stability which comprises the steps of establishingan electron flow, causing variations in magnitude of said flow toproduce two oppositely varying potentials causing said potentialscumulatively to effect said variations in magnitude of flow, and storingand releasing energy derived from said flow in time with the variationsthereof and applying the potential of said stored energy to increasesaid first mentioned potentials.

10. A vacuum tube oscillator comprising the combination with at leastone vacuum tube having an output electrode and a pair of controlelectrodes, of means for biasing said control electrodes to cause likechanges in the respective potentials thereof to produce opposite effectson the magnitude of current flow through the tube to said outputelectrode, a tuned oscillating circuit connecting said controlelectrodes, and an output circuit connected to said output electrode andcoupled to said tuned circuit.

11. In combination, an input circuit, vacuum tube relaymeans comprisingan output electrode anda pair of control elements, said control elementsbeing connected to said input circuit in opposed phase relationship,means for biasing said control elements to cause opposite potentialchanges impressed thereon to produce cumulative current-magnitudechanges in said relay means, an output circuit connected to said outputelectrodes and including a circuit element wherein variations ofpotential drop are produced by said cumulative current changes and meansfor applying said potential drop to said input circuit to produce saidopposite potential changes.

12. A vacuum tube oscillator comprising electron relay means providedwith a single output electrode and two control electrodes, an outputcircuit connected to said output electrode, a tuned input circuitconnected between said control electrodes, means for coupling the inputcircuit to the output circuit for feed-back of oscillating energy, andmeans for biasing said electrodes to cause said relay to operate withina range for which the output current-control potential curvescharacteristic of said two control electrodes are oppositely sloped.

13. A vacuum tube oscillator comprising electron relay means providedwith a single output electrode and two control electrodes, an outputcircuit connected to said output electrode, a tuned input circuitconnected between said control electrodes, means for coupling the inputcirouit to the output circuit for feed-back of oscillating energy, andmeans including a resistor connecting said input and output circuits tomaintain said control electrodes at a bias potential related to thepotential of said output electrode such that the output current-controlpotential curves characteristic of said control electrodes areoppositely sloped.

14. The method of controlling an electric current which comprisesgenerating an electron flow, establishing a pair of oppositely varyingpotentials differently positioned with respect to said flow, andmaintaining each of said potentials within a range of variation whereinsaid opposite variations have a cumulative effect on the magnitude ofsaid flow.

15. The method of operating a vacuum tube having a cathode, an anode,and a plurality of control electrodes, which comprises the steps ofmaintaining one of said electrodes at a mean potential whereat apositive variation thereof will produce an increase in electron flowthrough said tube, maintaining another of said control electrodes at amean positive potential whereat a positive variation thereof willproduce a decrease in said electron flow, and varying the potentials ofsaid control electrodes oppositely and simultaneously to produce acumulative effect on said flow.

16. A vacuum tube oscillator for producing electrical oscillationshaving a high degree of frequency stability, said oscillator comprisingthe combination with at least one vacuum tube having an output electrodeand a pair of control electrodes, of means for generating an electronflow in said tube and of means for impressing oppositely varyingpositive potentials on saidflow to provide variations in the rate ofelectron flow through the tube.

17. A vacuum tube oscillator comprising a vacuum tube having a cathode,an anode and a pair of control electrodes asymmetrically positioned withrespect to said cathode and anode, a resonant circuit connecting saidcontrol electrodes, an output circuit coupled to said resonant circuit,and means for imposing a common positive bias on said control electrodessuch that opposite changes of potential thereof produce cumulativechanges in magnitude of the output current of said tube.

RICHARD E. FURAY.

